The present invention relates to a video signal processing system and more particularly to a method and device for displaying a back-screen by using an on-screen signal while a video signal is not received.
Generally, the video signal processing system such as a color television receiver and a video tape recorder (VTR) has a blue back-screen processing function, in which the blue back-screen is displayed on a CRT (Cathode Ray Tube) screen to eliminate and prevent noise when the video signal is not received into the video signal processing system.
FIG. 1 is a block diagram illustrating a conventional video signal processing system with a blue back-screen generating circuit 40. A chrominance signal processing circuit 10 receives a composite video signal input to generate the R (Red), G (Green), B (Blue) primary color signals, a determination signal DET indicative of whether the video signal input is received or not, and horizontal and vertical synchronizing signals Hs, Vs. A compatible one-chip IC (Integrated Circuit) such as TDA 8362 by Philips company is usually used for the chrominance signal processing circuit 10.
In most cases, the determination signal DET is at the logic "low" at the time when the horizontal synchronizing signal Hs is detected from input signal received into the chrominance signal processing circuit 10. To the contrary, if the horizontal synchronizing signal Hs is not detected due to the non-reception of the video signal input, the determination signal DET is at the logic "high". The horizontal and vertical synchronizing signals Hs, Vs of the chrominance signal processing circuit 10 are respectively synchronized with the horizontal and vertical synchronizing signals of the video signal input when the video signal input is received. If, however, the video signal input is not received, the signals generated from a local oscillator in chrominance signal processing circuit 10 will take the place of the horizontal and vertical synchronizing signals Hs, Vs. A microcomputer 20 for controlling the system, receives the determination signal DET to generate a blue back-screen drive signal Bon for driving the blue back-screen when the determination signal DET indicates that video signal input is not received. The microcomputer 20 also generates an on-screen signal Son to display characters on the screen. A blue back-screen generating circuit 40 receives the blue back-screen drive signal Bon to displayed a blue screen. A CRT driver 30 receives the R, G, B primary color signals transmitted from the chrominance signal processing circuit 10 to drive a CRT to display an image of the video signal input on the screen or to display the CRT screen blue, in response to the output signal of the blue back-screen generating circuit 40. In addition, the CRT driver 30 can display characters on the screen according to the on-screen signal Son transmitted from the microcomputer 20.
The conventional device for displaying the blue back-screen includes a separate blue back-screen generating circuit, thus complicating the circuitry with the increased number of components.